1. Field of the Invention
The present invention relates to a door opening/closing device for controlling opening and closing of a door.
2. Description of the Related Art
An opening/closing device for controlling opening and closing of a door of a vehicle is provided with, for example, a slide door disposed on a side of a vehicle body. A driving unit drives the opening/closing device by transmitting a driving force of a motor to a rotational shaft via a clutch mechanism. A slide door is slid according to rotation of the rotational shaft. In the opening/closing device, the rotational shaft is rotatably supported to a case. The rotational shaft supports an output gear and a rotor rotated together therewith in the case. Within this case, a movable plate that is rotatable relative to the rotational shaft and can be engaged with and disengaged from a rotor is supported to the rotational shaft. An armature is fixed to the movable plate. An electromagnetic coil is fixed in the case to be opposed to the armature via the rotor. The electromagnetic coil forms a magnetically closed loop in cooperation with the armature and the rotor to attract the armature toward the rotor. Thus, the movable plate and the rotor are engaged with each other. Furthermore, the driving device includes, within this case, a rotary sensor including an annular magnetic body fixedly arranged outside the closed loop at an outer peripheral edge of the rotor and a hall element facing an outer peripheral face of the magnetic body for detecting rotation of the rotor (Japanese Patent Application Laid-open No. 2000-179233).
In the conventional door opening/closing device, since the magnetic body is fixedly arranged to the outer peripheral edge of the rotor, the magnetic body is arranged at the outermost peripheral position of a driving unit to take on a large annular shape. The hall element to detect the rotation faces the outer peripheral face of the magnetic body. Therefore, a distance between the magnetic body and the hall element in an axial direction of the rotational shaft or in a radially-outward direction tend to vary during rotation of the rotor. As a result, precision of the detection is degraded.
Moreover, the closed loop is formed by the armature and the rotor with an electromagnetic coil. Because the magnetic body is provided on the rotor, the magnetic body is practically affected by the closed loop. Therefore, in the conventional opening/closing device, magnetic flux of the magnetic body varies due to the magnetically closed loop. As a result, the precision of the detection is degraded.
Furthermore, in the conventional door opening/closing device, a main structure of the driving unit is arranged in a case to be integrated with a motor to form a driving unit assembly. The case is fixed to a body of a vehicle via a bracket. Therefore, the case should be a metallic case having rigidity. In addition, since the magnetic body is arranged on the outer peripheral edge of the rotor, and the hall element facing the outer peripheral face of the magnetic body is provided in the case. Therefore, a size of the case becomes large in a radially-outward direction of the rotational shaft and the weight of the entire device increases.